Methods and apparatus for leak detection in blood processing systems

ABSTRACT

A blood processing system includes a flow reversing device with at least an air sensor in the venous line located near the patient. During treatment, blood flow is reversed to cause air to infiltrate the blood lines if any disconnections or breaks in the blood line are present. One means for placing the sensor close to the patient is to provide the flow switching device aid sensors in a small lightweight module that can be located close to the treatment machine. Another is to provide a module with just the sensors near the access.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 10/578,600filed Mar. 31, 2008, now pending, which is a national stage ofInternational Application No. PCT/US2004/036933 filed Nov. 5, 2004,which claims the benefit of U.S. Provisional Application No. 60/518,122filed Nov. 7, 2003.

FIELD OF THE INVENTION

The present invention relates to the detection of leaks (includingneedle-disconnects and other causes of loss of integrity) inextracorporeal blood circuits and more particularly to the applicationof air infiltration detection techniques to the detection of leaks inpositive pressure return lines.

BACKGROUND

Many medical procedures involve the extraction and replacement offlowing blood from, and back into, a donor or patient. The reasons fordoing this vary, but generally, they involve subjecting the blood tosome process that cannot be carried out inside the body. When the bloodis outside the patient it is conducted through machinery that processesthe blood. The various processes include, but are not limited to,hemodialysis, hemofiltration, hemodiafiltration, blood and bloodcomponent collection, plasmaphresis, aphresis, and blood oxygenation.

One technique for extracorporeal blood processing employs a single“access,” for example a single needle in the vein of the patient or afistula. A volume of blood is cyclically drawn through the access at onetime, processed, and then returned through the same access at anothertime. Single access systems are uncommon because they limit the rate ofprocessing to half the capacity permitted by the access. As a result,two-access systems, in which blood is drawn from a first access, calledan arterial access, and returned through a second access, called avenous access, are much faster and more common. These accesses includecatheters, catheters with subcutaneous ports, fistulas, and grafts.

The processes listed above, and others, often involve the movement oflarge amounts of blood at a very high rate. For example, 500 ml. ofblood may be drawn out and replaced every minute, which is about 5% ofthe patient's entire supply. If a leak occurs in such a system, thepatient could be drained of enough blood in a few minutes to cause lossof consciousness with death following soon thereafter. As a result, suchextracorporeal blood circuits are normally used in very safeenvironments, such as hospitals and treatment centers, and attended byhighly trained technicians and doctors nearby. Even with closesupervision, a number of deaths occur in the United States every yeardue to undue blood loss from leaks.

Leaks present a very real risk. Leaks can occur for various reasons,among them: extraction of a needle, disconnection of a luer, poormanufacture of components, cuts in tubing, and leaks in a catheter.However, in terms of current technology, the most reliable solution tothis risk, that of direct and constant trained supervision in a safeenvironment, has an enormous negative impact on the lifestyles ofpatients who require frequent treatment and on labor requirements of theinstitutions performing such therapies. Thus, there is a perennial needin the art for ultra-safe systems that can be used in a non-clinicalsetting and/or without the need for highly trained and expensive staff.Currently, there is great interest in ways of providing systems forpatients to use at home. One of the risks for such systems is the dangerof leaks. As a result, a number of companies have dedicated resources tothe solution of the problem of leak detection.

In single-access systems, loss of blood through the patient access andblood circuit can be indirectly detected by detecting the infiltrationof air during the draw cycle. Air is typically detected using anultrasonic air detector on the tubing line, which detects air bubbles inthe blood. The detection of air bubbles triggers the system to halt thepump and clamp the line to prevent air bubbles from being injected intothe patient. Examples of such systems are described in U.S. Pat. Nos.3,985,134, 4,614,590, and 5,120,303.

While detection of air infiltration is a reliable technique fordetecting leaks in single access systems, the more attractive two-accesssystems, in which blood is drawn continuously from one access andreturned continuously through another, present problems. While adisconnection or leak in the draw line can be sensed by detecting airinfiltration, just as with the single needle system, a leak in thereturn line cannot be so detected. This problem has been addressed in anumber of different ways, some of which are generally accepted in theindustry.

The first level of protection against return line blood loss is the useof locking luers on all connections, as described in InternationalStandard ISO 594-2 which help to minimize the possibility of spontaneousdisconnection during treatment. Care in the connection and taping oflines to the patient's bodies is also a known strategy for minimizingthis risk.

A higher level of protection is the provision of venous pressuremonitoring, which detects a precipitous decrease in the venous linepressure. This technique is outlined in International Standard IEC60601-2-16. This approach, although providing some additionalprotection, is not very robust, because most of the pressure loss in thevenous line is in the needle used to access the patient. There is verylittle pressure change in the venous return line that can be detected inthe event of a disconnection, so long as the needle remains attached tothe return line. Thus, the pressure signal is very weak. The signal isno stronger for small leaks in the return line, where the pressurechanges are too small to be detected with any reliability. One way tocompensate for the low pressure signal is to make the system moresensitive, as described in U.S. Pat. No. 6,221,040, but this strategycan cause many false positives. It is inevitable that the sensitivity ofthe system will have to be traded against the burden of monitoring falsealarms. Inevitably this leads to compromises in safety. In addition,pressure sensing methods cannot be used at all for detecting smallleaks.

Yet another approach, described for example in PCT applicationUS98/19266, is to place fluid detectors near the patient's access and/oron the floor under the patient. The system responds only after blood hasleaked and collected in the vicinity of a fluid detector. A misplaceddetector can defeat such a system and the path of a leak cannot bereliably predicted. For instance, a rivulet of blood may adhere to thepatient's body and transfer blood to points remote from the detector.Even efforts to avoid this situation can be defeated by movement of thepatient, deliberate or inadvertent (e.g., the unconscious movement of asleeping patient).

Still another device for detecting leaks is described in U.S. Pat. No.6,044,691. According to the description, the circuit is checked forleaks prior to the treatment operation. For example, a heated fluid maybe run through the circuit and its leakage detected by means of athermistor. The weakness of this approach is immediately apparent: thereis no assurance that the system's integrity will persist, throughout thetreatment cycle, as confirmed by the pre-treatment test. Thus, thismethod also fails to address the entire risk.

Yet another device for checking for leaks in return lines is describedin U.S. Pat. No. 6,090,048. In the disclosed system, a pressure signalis sensed at the access and used to infer its integrity. The pressurewave may be the patient's pulse or it may be artificially generated bythe pump. This approach cannot detect small leaks and is not verysensitive unless powerful pressure waves are used, in which case theeffect can produce considerable discomfort in the patient.

Clearly detection of leaks by prior art methods fails to reduce the riskof dangerous blood loss to an acceptable level. In general, the risk ofleakage-related deaths increases with the decrease in medical staff perpatient driven by the high cost of trained staff. Currently, with lowerstaffing levels comes the increased risk of unattended leaks. Thus,there has been, and continues to be, a need in the prior art for afoolproof approach to detection of a return line leak or disconnection.

In an area unrelated to leak detection, U.S. Pat. No. 6,177,049 B1suggests the idea of reversing the direction of blood flow for purposesof patency testing. The patent also states that flow reversal may beused to improve patency by clearing obstructed flow.

U.S. Pat. No. 6,572,576 discusses various embodiments of a bloodtreatment device where blood flow is reversed to provide leak detection.According to the inventions described, a leak detector effective toensure detection of leaks in the venous blood line (the line returningblood to the patient) is provided by periodically generating a negativepressure, which may be brief or at a 50% duty cycle, in the blood returnline. This draws air into the venous line which can be revealed by anair sensor in the blood treatment machine. During the negative pressurecycle, any air drawn in the venous blood line is detected, the system isshut down and an alarm generated. U.S. Pat. No. 6,572,576, filed Jul. 7,2001 entitled “Method and apparatus for leak detection in a fluid line”is hereby incorporated by reference as if fully set forth in itsentirety herein.

Hemofiltration, dialysis, hemodiafiltration, and other extracorporealblood treatments may employ flow selector valves such as Y-valves,four-way valves, and other such devices for redirecting the flow ofblood and other fluids such as replacement fluids. For example, thedirection of the flow of blood through certain types of filters may bereversed repeatedly to prevent coagulation of blood in regions where themean flow slows to very low rates. For example, where blood iscirculated through tubular media in the context of a dialysis filter, ithas been proposed that blood may coagulate on the surface of the inletheader leading to the progressive coagulation of blood. U.S. Pat. No.5,605,630, proposes occasionally reversing the flow of blood through thefilter. A four-way valve is proposed for changing over the flowdirection.

In other references, the idea of reversing the flow of blood through atubular media filter is discussed in connection with other issues. Forexample, in U.S. Pat. No. 5,894,011, the known technique of switchingaccess lines in the patient to improve the flow through an occludedfistula is automated by the addition of a four-way valve on thepatient-side blood circuit. In single-access systems in general, forexample as described in U.S. Pat. No. 5,120,303, flow is conventionallyreversed through the filter during each draw/return cycle. In the '303reference, the specification observes that the efficiency of filtrationis increased due to the double-passing of the same blood through thefilter; that is, each volume of drawn blood is filtered twice. Yetanother reference, U.S. Pat. No. 6,189,388 B1, discusses reversing theflow direction of blood through the patient access occasionally in orderto quantify an undesirable short-circuit effect that attends their longterm use. Still another U.S. Pat. No. 6,177,049 B1 suggests reversingflow through the draw access before treatment while an observer ispresent to test the accesses for patency or to clear blockage in theaccesses.

Referring to FIGS. 1A through 1E, a number of alternative designs forfour-way valves have been developed for blood circuits. Referring toFIG. 1A, U.S. Pat. No. 5,894,011, discloses a valve that swaps theconnections between pairs of lines 905 and 906 via a pair of rotatablyconnected disks 901 and 902, each of which supports one of the pairs oflines 905 and 906. A seal must be maintained between the disks 901 and902 and between the respective lines. The device is intended to beoperated manually.

Referring to FIG. 1B, another four-way valve, disclosed in U.S. Pat. No.5,605,630, which has been proposed for use in blood lines, has arotating wheel 910 with channels 911 and 912 defined between the wheel910 and the inside of a housing 913. When the wheel is rotated, thechannels 911 and 912 shift to join a different pair of lines. Thisdevice also has seals.

Referring to FIG. 1C, another arrangement is proposed in U.S. Pat. No.6,177,049. This device has a rotating component 915 with channels 921and 922 defined within it. As the rotating component 915 is rotated, thechannels defined between pairs of lines 917 and 919 change from parallellines joining one set of corresponding lines to U-shaped channelsjoining a different set.

Referring to FIGS. 1D1 and 1D2, a design, disclosed in U.S. Pat. No.4,885,087, is very similar to that of FIG. 1B. This design has a rotator925 that connects different pairs of lines depending on the positionthereby defining two different sets of possible flow channels 926 and929 or 927 and 931.

In all of the above designs, the valves are not hermetically sealed. Anyseal can be compromised, particularly by microorganisms. Thus, each ofthe foregoing designs suffers from that drawback. Also, many areexpensive and do not lend themselves to automation.

Referring to FIG. 1E, another type of four-way valve is formed byinterconnecting two tubes 937 and 938 with crossover lines 935 and 936.This design is disclosed in U.S. Pat. No. 6,189,388 (Hereafter, “U.S.Pat. No. '388”). Tube pinching actuators 941-944 are used to force fluidthrough different channels, depending on which actuators are closed.This device provides a hermetic seal and can be fairly inexpensive, butin a given configuration, significant no-flow areas are defined. Thesedead spaces can lead to the coagulation of blood, which is undesirable.Also, the interconnection of tubes in this does not lend itself toautomated manufacturing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, 1C, 1D1, 1D2, and 1E illustrate various flow reversingdevices according to the prior art.

FIG. 2A illustrates a flow circuit including a blood treatment machineand a sensor module.

FIG. 2B illustrates a flow reversing portion of the blood treatmentmachine of FIG. 2A.

FIG. 3A illustrates a flow circuit including a blood treatment machine,a flow reversing module.

FIG. 3B illustrates features of the flow reversing module of FIG. 3A.

FIG. 3C illustrates a flow circuit including a blood treatment machine,a flow reversing module, and a sensor module.

FIG. 3D illustrates details of a sensor module.

FIG. 3E illustrates a detail of a flow circuit with a flow reversingmodule and separate sensor modules.

FIG. 4A illustrates a portion of a fluid circuit that is interoperablewith an actuator to form a flow reversing device.

FIG. 4B illustrates an actuator interoperable with the fluid circuitportion illustrated in FIG. 4A.

FIGS. 5A and 5B illustrate two operating modes of a flow reverserdefined by the combination of the devices of FIGS. 4A and 4B.

FIG. 6 illustrate a flow reversing actuator according to an alternativeembodiment to that of FIGS. 4A, 4B, 5A, and 5B.

FIG. 7 illustrates a flow reversing device according to an alternativeembodiment to that of FIGS. 4A, 4B, 5A, and 5B.

FIG. 8A illustrates a sensor module embedded in a soft outer casing.

FIG. 8B illustrates a compact longitudinal reversing module.

FIGS. 9A-9C illustrate a first embodiment of a fluid circuit portion andan actuator for providing a compact longitudinal flow reverser.

FIGS. 10A and 10B illustrate a second embodiment of an actuator forproviding a compact longitudinal flow reverser.

FIG. 11 is a flow chart for describing a control embodiment in whichblood flow is reversed according to multiple schedules.

FIG. 12 is a time plot of blood flow for use in describing the controlregime of FIG. 11.

FIG. 13 is an illustration of stagnant flow regions for illustrating theflow control regime of FIGS. 11 and 12.

FIGS. 14A and 14B illustrate control responses to air detection,according to an embodiment of the invention.

DESCRIPTION OF THE EMBODIMENTS

Referring now to FIG. 2A, a patient 130 is connected by an access 139 toa blood processing machine 315. The latter draws blood through anarterial blood line 305 and returns treated blood to the patient 130through a venous blood line 307. The blood processing machine 315 may beany treatment device such as a hemodialysis machine, a hemofiltrationmachine, an infusion pump (in which case no arterial line 305 would bepresent), etc.

Access 139 may consist of various devices such as a fistula (not shown)and catheter (not shown) combination or other type of access which maybe disconnected by various means. For example, a catheter (not shown)may be withdrawn from a fistula (not shown) and/or the catheter (notshown) disconnected from the arterial 307 and venous 305 lines by meansof a luer connector (not shown). The above are conventional features ofwhich a variety of alternatives are known.

One or more bubble or air sensors (not shown) are provided in a sensormodule 311. The sensor module 311 is connected to the blood processingmachine 315 by means of a signal line 302. The signal line 302 applies asignal indicating the presence of air or bubbles in one or both of thearterial 307 and venous 305 lines. The sensor module 311 may belightweight snap-on module that clamps onto the arterial 307 and venous305 lines. As is common in blood treatment systems, the arterial 307 andvenous 305 lines are clear plastic such as PVC. The sensor module 311may also include a sensor to indicate the presence of blood in thearterial 307 and venous 305 lines as well. The latter signal may be usedfor indicating and controlling a transition from a priming mode wherethe arterial 307 and venous 305 lines carry sterile fluid to a treatmentmode where the arterial 307 and venous 305 lines carry blood.

Referring now also to FIG. 2B, the blood processing machine 315 mayinclude, along with various other hardware elements, a flow reversingvalve 327. The flow reversing valve 327 may be controlled by anelectronic controller 323 to cause the flow through the arterial 307 andvenous 305 lines to reverse. In a normal treatment mode, the flow may beas indicated by arrows 301A and during a test mode, in which flow isreversed, blood flow may be as indicated by arrows 301B. During bothtreatment and test modes, the flow of blood on the other side of thereversing valve 327 may remain as indicated by arrows 301C.

During treatment, the reversing valve 327 is periodically actuated toplace the reversing valve 327 in the test mode. This generates anegative gage pressure in the venous line 305. If any leaks are presentin the venous line 305 between the patient 130 and the sensor module311, air will infiltrate the venous line 305 and be detected by the airor bubble detector within the sensor module 311. The resulting signalmay be applied to the controller 323. The controller 323 may beconfigured to respond by controlling one or more line clamps asindicated at 317 to stop the flow of blood and trigger an over-pressurealarm in the blood processing machine 315 if the latter is provided withone. The controller may also activate an alarm (not shown). Thecontroller may alternatively maintain the test mode to continue flow inthe reversed direction in which case, if the blood processing machine315 is provided with an internal air or bubble detector (not shown), thelatter will be triggered by the infiltrating air as if the air had beendrawn by the arterial line in the first instance.

Although a flow reversing valve 327 is illustrated in FIG. 2B,alternative mechanisms for generating a negative pressure in the venousline 305 as discussed in references incorporated by reference in theinstant specification. Also, while one line clamp 317 is illustrated,more clamps may be employed to prevent the loss of blood. For example, aclamp may be provided in the venous line 305. Note that the use of asensor module 311 as illustrated allows the sensors to be located closeto the patient. Consequently, the system can respond quickly to adisconnection of the arterial 307 or venous 305 lines. One of the commontypes of leaks the system may protect against is an improperly installedor defective connection between the venous 305 or arterial 307 line andthe catheter (not shown).

Referring now to FIGS. 3A and 3B, a combined flow reversing and sensormodule 333 houses a flow reversing valve 351 and at least one sensor352A. Flow through venous 325 and arterial 327 lines may be reversed inportions 337 and 335, respectively, by reversing the flow reversingvalve 351. The sensor 352A may include a bubble or air sensor, a bloodsensor, or both. The sensor module 333 or any of the other sensormodules described herein may include other types of sensors such aspressure sensors to detect a loss of patency at any point in the system.In the foregoing embodiments, the blood or air (or bubble) sensors mayinclude non-wetted conductivity sensors or non-wetted conductivity cellssuch as optical (opacity or hue) sensors or any sensor suitable fordetecting the presence of air or blood in a clear liquid. The sensormodule may also be used to detect other properties or conditions nearthe patient access such as a sudden acceleration (by means of anaccelerometer) due to detachment and subsequent falling out of acatheter, for example. An additional sensor 352B, which may be identicalto sensor 352A, may be employed to provide an indication of airinfiltration during normal operation in a forward blood-flow direction.

A controller 349 may be provided to periodically control the flowreversing valve 351. The controller may activate a line clamp 326. Thecontroller may respond to the detection of air in the same manner asdescribed with respect to the foregoing embodiments or as described inthe references incorporated in the instant specification, for example,by clamping the line. A signal line 329 may be provided to transmitdetector and/or controller signals to the blood processing machine 320.Blood processing machine 320 may be similar to that described withreference to the previous embodiments (e.g. 315 in FIGS. 2A and 2B), butpreferably it does not include the reversing valve 351. As in previousembodiment, in a normal treatment mode, the flow may be as indicated byarrows 301A and during a test mode, in which flow is reversed; bloodflow may be as indicated by arrows 301B. During both treatment and testmodes, the flow of blood on the other side of the reversing valve 351may remain as indicated by arrows 301C.

Referring now to FIG. 3C, the blood processing machine 320, the same asthe one described with reference to FIG. 3A, is linked by venous 373 andarterial 375 blood lines to a flow reversing module 370. A sensor module377 is located close to the access 139 and is coupled to the reversingmodule 370 by a signal line 378. Venous 374A and arterial 376A lineslink the reversing module 370 to the access 139 for supply and returnflows of blood (with reference to the patient 130), respectively.Portions of venous 374B and arterial 376B lines pass through the sensormodule 377 to the access 139. The configuration of FIG. 3C, as in theconfiguration of FIGS. 2A and 2B allows the sensor module 377 to belocated close to the patient 130 and for the reversing module 370 to beretrofitted to a blood treatment machine 315 that is otherwise notconfigured for leak detection in the fashion described. Thus FIGS. 3A-3Care attractive for retrofit applications where leak detection capabilityis to be added to a blood processing machine 315 otherwise notconfigured for it.

Internally, the flow reversing module 370 may be identical to that shownin FIG. 3B. The sensor(s) 352 may or may not be present to protectagainst leaks in the portions of the venous and arterial lines 374A and376A as well as the portions 374B and 376B which are protected bysensors in the sensor module 377. Note also that signal line 378 or anyof the foregoing signal lines may represent wireless links, acousticalsignal links, or any suitable means of communication. Also, the variousdevices may be powered by battery or by electrical lines.

Referring to FIG. 3D, a sensor module 380 has features which may beemployed in sensor modules 311 (FIG. 2A) and 377 (FIG. 3C) describedabove. Air detectors 401 and 407 detect air passing through lines 374and 376, respectively. Blood sensors 403 and 405 may be included in thesensor module 380 to detect blood in lines 374 and 376, respectively.Note that in another embodiment, the sensor module 380 only containssensors for a single line 374, which is preferably the venous line ofthe foregoing embodiments. In yet another embodiment, the entire sensormodule 380 is connected around a single line 374, which is preferablythe venous line of the foregoing embodiments. In the latter case, onlythe upper part 380A is present and the other half 380B on the other sideof line 380C is not present. Note that alternatively, both lines may beprovided with separate sensor modules 390A and 390B in an alternativeembodiment as illustrated at FIG. 3E. Note also that two adjacent flowlines may be protected by a single air detector or blood detector orboth.

A key 409 of any desired shape may be placed on one of the lines 374 or376 which fits into a slot 411 and engages a detector 410 to indicateits proper insertion into the slot 411. The key 409 and slot 411 ensurethat if only one line 374 is protected by air sensor 401, that it is thevenous line. Otherwise the protection system wherein flow is reversed toindicate a leak would serve no purpose. The detector 410 may send asignal along the signal line 378 to indicate proper insertion. A failureof proper insertion while attempting to operate the system may cause thesystem to generate an alarm. A door 406 may be closed over the lines 374and/or 376 to lock them in place. Electronic equivalents of key 409 andsensor 410 may also be provided.

Referring to FIGS. 4A and 4B, in an embodiment of a compact and reliableflow reversing device, a portion of a fluid circuit 224 includes atoroidal portion 226 with ports A, B, C, and D linked by segments 221A,221B, 221C, and 221D as illustrated. Fluid lines 203, 205, 207, and 209connect with respective ones of ports A, B, C, and D. The toroidalportion and portions of fluid lines 203, 205, 207, and 209 fit intochannels 211, 215, 211, and 217 of an actuator 221. The actuator 221contains a rotatable clamp 222 with two edges 238 and 237 whichselectively pinch segments 221A, 221B, 221C, and 221D between the edges238 and 237 and edges 231, 229, 235, and 233 of the actuator 221,respectively as illustrated in FIGS. 5A and 5B.

Referring now to FIG. 5A, the toroidal portion 226 may be of a compliantand stretchable material that permits it to be forced into position inthe actuator 221 and partly deformed as illustrated. The clamp 22 may bein the neutral position illustrated in FIG. 4B when this is done. Duringoperation, when clamp 222 is in a first position indicated in FIG. 5A,segments 221B and 221D are clamped closed allowing a flow between line209 to 207 and from line 205 to line 203 as indicated by arrows 225A and227A. As will be observed, segment 221B is pinched between edges 238 and231 while segment 221D is pinched between edges 237 and 235. The path oflines 209 to 207 may correspond to flow through the venous lines of theprevious embodiments. For example, with reference to FIG. 3A, line 209may correspond to line 325 and line 207 to line 337. Similarly, the pathof lines 205 to 203 may correspond to flow through the arterial lines ofthe previous embodiments. For example, with reference to FIG. 3A, line205 may correspond to line 335 and line 203 to line 329. In theconfiguration of FIG. 5A, the flow may then provide for normal bloodflow for treatment by allowing 207 to flow blood to a patient and returnthrough line 205 to pass through the flow reverser back to a bloodtreatment machine.

Referring now to FIG. 5B, when clamp 222 is in a first positionindicated in FIG. 5B, segments 221A and 221C are clamped closed allowinga flow between line 209 to 205 and from line 207 to line 203 asindicated by arrows 225B and 227B. In the configuration of FIG. 5B, theflow may then provide for reverse blood flow for testing by allowingline 205 to flow blood to a patient and return through line 207 to passthrough the flow reverser back to a blood treatment machine. Thisresults in a negative pressure in line 207 whereupon if anydisconnections or leaks occur, air will be drawn into line 207 which maybe revealed by a sensor, as discussed with reference to the figuresabove.

Referring now to FIGS. 6 and 7, in alternative embodiments of the flowreverser of FIGS. 5A and 5B a clamp 427 may be passively mounted on adoor 424 and engaged with a drive bolt 443 in a chassis portion 421 of aflow reverser. The drive bolt 443 may fit as a key in a recess 441thereby driving the clamp. The closure of the door 424 may be indicatedby a detector which may send a signal to a controller permitting thedrive bolt 443 to be operated according to the configuration of acontroller (e.g., 349 of FIG. 3B). Instead of a single rotating clamplocated at a center of a flow reverser, respective clamps 451A, 451B,451C, and 451D may pinch respective portions of the flow circuittoroidal portion 226 by means of a shaped boss 449 that fits into thecenter of the toroidal portion 226. The claims 451A, 451B, 451C, and451D may be operated by respective drives such as solenoids (not shown)or coupled to be operable with one or two drives as desired.

Referring to FIG. 8A, to permit a flow reverser or sensor module to beplaced close to the patient but allow for patient comfort, the flowreverser or sensor module 379 may be fitted into a soft shell 501. Thelatter may have a shape such as a teddy bear or other stuffed animal orornament.

Referring to FIG. 8B, preferably the flow reverser is of a compactlongitudinal shape with the lines 667 and 669 leading to the bloodtreatment machine stemming from one end and the lines and the lines 663and 665 leading to the patient access stemming from the opposite end.This may allow the flow reverser 661 to lie close to the patient accessand self-orient in a comfortable and unobtrusive manner.

Referring to FIGS. 9A, 9B, and 9C, two Y-junctions 503 and 505 may beconnected to a patient access and two other Y-junctions may be connectedto a blood treatment machine or remainder thereof. Two double edgedclamps 519 and 521 are driven by a double-axis motor drive 527 thatrotates one clamp 519 in one direction and the other clamp 521 in theopposite direction, for example by providing that one clamp is connectedto the stator and one connected to the rotor of the motor. It iscontemplated that a reduction drive would be employed to increase thetorque of the primary motor within the drive 527 and allow a small motor(not shown separately) to be used. A support stalk 502 holds the drive527 so that it is free to rotate with respect to it, thereby providing amounting to a housing such as illustrated in FIG. 8B. Each segment 511,513, 515, and 517 may be selectively pinched by as illustrated in FIGS.9B and 9C to provide for forward and reverse flow between one pair ofjunctions 505/503 or 509/507. The clamps may be tapered to provide ahigh clamping pressure as indicated at 535, 533, 523, and 525 andsimilarly on portions opposite the edges indicated at 535, 533, 523, and525.

Note that the tubing structure of FIG. 9A which includes parallelsegments 511, 513, 515, and 517, and the four Y-junctions 503 and 505,507, and 509, is toroidal in shape, which can be confirmed byinspection. It will be observed that a planar projection (that is, amapping or projection, as of a shadow, onto a plane, as of a shadow ontoa surface) of the structure 511, 513, 515, and 517, 503, 505, and 507with a plane perpendicular to parallel segments 511, 513, 515, and 517and a projection direction parallel to parallel segments 511, 513, 515,and 517, is shaped as a ring.

Referring to FIGS. 10A and 10B, another flow reversing device using afluid circuit portion as illustrated in FIG. 9A producing four parallelsegments 511, 513, 515, and 517 is driven by a linear drive (not shown)that moves a stalk 607 along an axis thereof. Cams 617 and 619 areforced into an opposing pair of tube segments 605 and 611 when a largediameter portion 627 of the stalk 607 is forced between the cams 617 and619 by pushing the stalk 607 in a first direction (to the left). Cams617 and 619 are forced into an opposing pair of tube segments 633 and635 when a large diameter portion 627 of the stalk 607 is forced betweenthe cams 610 and 621 by pushing the stalk 607 in a second oppositedirection (to the right). The segments may be held in position by aframe of two portions 613 and 615 which close around a cam frame 607.Edges 609 and 611 are provided to amplify the pinching stress andcooperative with cams 617 and 619 to clamp the tubes segments 603 and609.

Referring to FIG. 11, an operating regimen begins with a priming of afluid circuit at step S10. The priming mode is initiated by a primingcommand being received by the flow reverser controller at step S10. Theflow reverser controller places the flow reverser in forward mode sothat fluid is pumped in a single direction. The controller may beconfigured to operate for flow in a single direction continuously aslong as no blood is detected by blood sensors in the sensor module or inthe blood treatment machine. The pump may be operated at step S20 for adesired period of time to prime the blood circuit and other portions ofthe fluid circuit used for treatment. At some point during the primingmode, the operator may halt the pump, clamp various lines, and makecertain connections in preparation for treatment and restart the pump.All these steps are assumed to fall within step S20.

When the flow reverser controller detects blood in step S25, controlflow exits to step S30 and flow continues in the same direction for aspecified period of time which may be proportional to the mass flow rateof blood. The blood will ordinarily be detected because of theconnection changes of the operator who has determined that the system isadequately primed and has remade connections as required. This may alsobe an automated process as well depending on the blood processing systemand the level of automation. Referring now also to FIG. 12, once theinitial forward operation period has elapsed at step S30, the flowreverser control may go into an operating mode where it periodicallyreverses flow 830 for a fixed interval test cycle 820 to generate atemporary negative pressure and reverse flow to test the venous line andthen returns to forward operation 835. Generally, the test cycle 820interval will be shorter than the normal forward treatment 825 interval.In addition to the test cycle, short duration reverse cycles 810 are ahigher frequency may be included to clear the dead legs of the flowreversing device. Referring momentarily to FIG. 13, the shaded regions815 in the embodiment of FIGS. 5A and 5B in the normal flow directionrepresent areas with no flow. If the blood in these regions is allowedto stagnate for an extended time, clotting may occur. To help preventthis, the flow may be reversed for very short intervals to cause a flowin these otherwise continuously non-flow regions 855. A train of suchdead-leg clearing cycles is shown in FIG. 12 at 810.

Returning to FIG. 11, the cyclical operation of FIG. 12 may continueuntil a treatment is completed or until air is detected (or some othermalfunction causes treatment to be terminated). For retrofit embodimentsof the flow reversing leak detection system such as illustrated in FIGS.3A and 3C for example, it is desirable for the flow reversing controllerto respond to air detection in a manner that ensures an appropriateresponse without some sort of control connection or controlcollaboration between the flow reversing module (e.g. 370, FIG. 3C) andthe blood treatment machine 320. Thus, preferably the flow reversingmodule control's 349 response should ensure appropriate action.Referring now to FIG. 14A, to that end a response S45A for step S45,when air is detected at step S40, the blood lines may be clamped at stepS60 to induce a high pressure in the blood treatment machine which inmost type of blood treatment machines would trigger a shutdown and errorindication by the machine. This may be provided by means of a clamp asindicated at 326 or 317 in FIGS. 3B and 2B respectively, for example.Referring to FIG. 14B, another response for step S45 is step S45A inwhich a shutdown by the main processing machine is induced in step S65to continue operating in reverse mode until the air that was detected bythe flow reversing module triggers an air detection by the bloodprocessing machine.

Note that by placing the air sensor close to a patient as described inthe foregoing embodiments, the reverse cycle may be kept to a minimumduration. Preferably this duration is established to provide the minimumvolume displacement needed to cause any air bubbles leaking into theblood line to reach the air sensor in the sensor module. This may beestablished in the flow reverser by means of an input from a user or bycalculating from a measured flow rate. Thus, a flow rate sensor may beincluded in the flow reversing module and the controller configured tocalculate the amount of time, based on flow rate, to ensure the minimumvolume is displaced.

The invention claimed is:
 1. A flow control valve, comprising: aflexible valve body linking together, for fluid communication, fluidports fluidly connected by said valve body; a first portion of anactuator with at least one first pinching element; a second portion ofsaid actuator that moves relative to said first portion; said valve bodyforming a structure that surrounds the first portion, said valve bodybeing at least partly confined within the second portion said secondportion having at least one second pinching element opposing said atleast one first pinching element; in a first configuration, saidactuator pinching said valve body such that a first pair of said fluidports are linked for fluid communication while a second pair is blocked;in a second configuration, said actuator pinching said valve body suchthat said second pair of said fluid ports are linked for fluidcommunication while said first pair is blocked.
 2. A valve as in claim1, wherein a planar projection of said valve body is ring-shaped.
 3. Ablood flow reversing device for blood processing, comprising: a pair ofpatient-side ports for connection to a patient access; a pair oftreatment-side ports for connection to a blood processing machine; areversing valve configured to allow blood to flow between saidpatient-side and said treatment-side ports in two selected directions offlow, such that blood flow from said patient-side ports and said patientaccess is selectively reversible; a controller configured to controlsaid reversing valve and to reverse said blood flow for a first intervalat a first frequency and for a second interval at a second frequency,said first frequency being greater than said second frequency, whereinthe reversing valve has a flexible valve body that forms a structuresurrounding a first portion of an actuator with at least one firstpinching element, a second portion of said actuator is constructed tomove relative to said first portion and has at least one second pinchingelement opposing said at least one first pinching element, in a firstconfiguration, said actuator pinches said valve body such that a firstpair of said ports is linked for fluid communication while a second pairis blocked, and in a second configuration, said actuator pinches saidvalve body such that the second pair of said ports is linked for fluidcommunication while the first pair is blocked.
 4. A device as in claim3, wherein said second interval is longer than said first interval.
 5. Adevice as in claim 3, further comprising a housing having said patientside ports on a first end and said treatment-side ports on a second end,whereby said flow reversing device may be located close to said patientaccess and remote from a blood treatment machine.
 6. A device as inclaim 5, further comprising an air detector.
 7. A device as in claim 5,further comprising an air detector, said reversing valve beingconfigured to block blood flow through said treatment-side ports andsaid controller being configured to control said reversing valve toblock said blood flow in response to a detection of air in blood by saidair detector.